A Simple Time-Resolved Optical Measurement of Diffusion Transport Dynamics of Photoexcited Carriers and Its Demonstration in Intrinsic GaAs Films

We develop a tightly focused pump-probe absorption technique to study diffusion dynamics of photoexcited carriers. It has many advantages including the simple setup and operations, higher detection sensitivity, an analytic descriptive model and fast data samplings. Diffusion dynamics are measured twice, separately using two different-sized probe spots, instead of many time-delayed diffusion profiles of a carrier pocket measured using spatially probe-spot scanning. An analytic model is derived to describe diffusion dynamics. Diffusion dynamics in GaAs are measured to demonstrate the feasibility of this technique. The diffusion coefficient is obtained and agrees well with the reported experimental and theoretical results.